1.Southwest Electric Power Design Institute Co. , Ltd. , CPECC, Chengdu 610056, China
2.Key Laboratory of Meteorological Disaster, Ministry of Education/Joint International Research Laboratory of Climate and Environment Change/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science & Technology, Nanjing 210044, China
3.Fujian Key Laboratory of Severe Weather and Key Laboratory of Straits Severe Weather, China Meteorological Administration, Fuzhou 350001, China
Based on the assimilation module for Himawari-8 AHI radiance data in the weather research and forecasting model data assimilation (WRFDA) system with WRF model, this paper investigated the impact of direct assimilation of the radiance data of the three water vapor channels from Himawari-8 AHI on the forecast of a heavy rainfall in Northeast China. The results show that the quality control and bias correction are effective in eliminating anomalous data, making the mean of observation minus background (OMB) closer to 0, while the standard deviation and root mean square error of observation minus analysis (OMA) are further reduced. Compared with the control experiment, after assimilating AHI radiance data, the root mean square errors are reduced by about 0.2 m/s and 0.1 K in the middle and lower layers for the wind and temperature respectively, and the root mean square error of specific humidity decreases by about 0.03 g/kg in the lower layers. Besides, the assimilation of satellite data contributes positively to the increment of relative humidity in the central part of Jilin Province. The final forecast of 3 h precipitation is improved. The experiments involving satellite data assimilation show an improvement in the ETS and bias scores exceeding 0.1 of all thresholds. For the 50 mm threshold, the improvement rates for ETS and bias scores reach 64% and 58%, respectively. In addition, the assimilation of AHI radiation data enhances the alignment of the hourly precipitation forecast trends at a single observation station with the actual observations.
试验模拟时间段为2017年7月12日0时—14日0时。2017年7月12日0—6时进行6 h spin-up。针对热启动后6 h的预报场,进行两组不同的试验:一组直接以2017年7月12日6时的预报场作为初值场,积分42 h至14日0时,记为CTL试验;另一组以2017年7月12日6时的预报为同化的背景场,6—12时逐小时进行同化,以最后一次同化的分析场为模式的初值场,从12时开始预报36 h至14日0时,记为AHI试验。
3 试验结果分析
3.1 偏差订正
AHI试验中通道8~10的辐射率资料被同化。7月12日6时偏差订正前、后观测亮温减去背景场模拟的亮温(OMB,observation minus background)和偏差订正后观测亮温减去分析场模拟的亮温(OMA,observation minus analysis)可知(图2),偏差订正前模式西南区域卫星OMB值整体偏高。偏差订正,尽管大部分扫描点OMB的绝对值仍较大,但较高的OMB值得到一定程度的矫正,较偏差订正前更接近0 K。在同化后的分析场中大部分扫描点OMA的绝对值进一步接近0 K,说明分析场相对背景场更接近观测,表明同化是有效的。
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